394 AGRICULTURAL ANALYSIS 



a filter into a capsule with a flat bottom, in which the evapora- 

 tion is finished on a steam-bath, taking care that the tempera- 

 ture does not exceed 100. An important precaution is not to 

 allow the contact of the water with the soil to be too prolonged, 

 to avoid the reduction of the nitrates which could take place 

 under the influence of the denitrifying organisms which are de- 

 veloped with so great a rapidity in moist earth. The apparatus 

 in which the transformation of the nitrates into nitric oxid takes 

 place is essentially that already described (Fig. 20). The car- 

 bon dioxid generator is connected by means of a rubber tube 

 and a small wash-bottle to the small retort in which the reaction 

 takes place, and from which the exit tube leads to a mercury 

 trough. The gas which is disengaged is received under a jar 

 drawn out to a fine point in its upper part, which carries about 

 15 cubic centimeters of potash solution containing two parts of 

 water to one of potash. 



The operation is conducted as follows: 



Into the small capsule which contains the dried matter, three 

 or four cubic centimeters of ferrous chlorid are poured. By 

 means of a stirring rod the residue sticking to the sides of the 

 capsule is detached with care, and all the matter is thus collected 

 in the bottom. By means of a small funnel the contents of the 

 capsule are introduced into the retort. About two cubic centi- 

 meters of hydrochloric acid are used for washing out the mate- 

 rials, and this acid is also introduced into the retort. The wash- 

 ing with hydrochloric acid is repeated three or four times, and 

 finally the apparatus is washed with one cubic centimeter of 

 water, which is also poured in by the small funnel with great 

 care, so that this water may form a layer over the surface of the 

 liquid. The apparatus is now connected and filled completely 

 with carbon dioxid. Since it is necessary that this gas should 

 be completely free of air, the flask which generates it is first 

 filled with the acidulated water from the acid flask, and the air 

 is thus almost totally displaced by the liquid. The evolution of 

 carbon dioxid gas which follows, completely frees the apparatus 

 from air. When this is accomplished the retort is connected 

 with the rest of the apparatus and the gas allowed to pass for 



